Conventionally, an image forming apparatus adopting an electrophotographic system has been provided with a cleaning device for removing toner remaining on a photoreceptor serving as an electrostatic latent image carrier. Because of space-saving, design simplicity, mechanism simplicity, and/or other reasons, a cleaning device that is frequently used today uses a blade (cleaning blade) that scrapes toner by making contact with a surface of a photoreceptor.
However, as a recent image forming apparatus operates at a higher speed, the use of a cleaning device with a blade causes a photoreceptor to have a short life span. The reason for this is that: the increase in the operation speed results in a higher processing speed, and this increases an abrasion (decrease in film thickness) of a surface, which makes contact with the blade, of the photoreceptor.
An abrasion of a surface of a photoreceptor may be suppressed, for example, by reducing a coefficient of friction. The following describes examples of conventional techniques for reducing a coefficient of friction.
Japanese Unexamined Patent Publication No. 70196/2005 (Tokukai 2005-70196; published on Mar. 17, 2005) describes a technique in which (i) a plurality of cuts are formed in a portion, which makes contact with a photoreceptor, of a blade and (ii) the cuts are impregnated with a lubricant (zinc stearate). Further, the photoreceptor is provided with a protective layer containing inorganic fine particles made up of alumina or titanium oxide.
Further, Japanese Unexamined Patent Publication No. 86142/2004 (Tokukai 2004-86142; published on Mar. 18, 2004) describes a technique in which a fluorocarbon resin layer is provided as an outermost surface layer of a photoreceptor so that a void on a surface of the photoreceptor is filled with the fluorocarbon resin layer.
Japanese Unexamined Patent Publication No. 72957/1993 (Tokukaihei 5-72957; published on Mar. 26, 1993) describes a technique in which a process for low friction is carried out by (i) adding a fluorocarbon resin into an image area portion of an edge, which makes contact with a photoreceptor, of a blade (mixing a fluorocarbon resin into a blade material) or (ii) applying fluorocarbon paint or silicon paint to the image area portion.
Further, a high-speed machine and a color machine, which have been recent mainstream types of image forming apparatus, use toner (small-particle toner) having a small particle diameter of approximately 5 μm.
However, the conventional arrangements, respectively disclosed in Tokukai 2005-70196, Tokukai 2004-86142, and Tokukaihei 5-72957, in which a coefficient of friction is reduced suffer from the following problems: (1) an effect of reducing the friction of a photoreceptor is insufficient; (2) the reducing effect is not retained; (3) a cleaning property is reduced; and/or (4) electrophotographic performance is degraded.
Specifically, the arrangement, disclosed in Tokukai 2005-70196, in which the cuts are formed in the blade and impregnated with the lubricant is ineffective in reducing a coefficient of friction. This is because each part (having a width of approximately 1 mm) between adjacent cuts is not impregnated with the lubricant. Further, the process of forming the small cuts in the blade requires high accuracy. This raises problems that manufacturing cost is increased and that the blade is likely to be damaged.
Further, the arrangements in which a photoreceptor is processed for the purpose of reducing a coefficient of friction (i.e., (i) the arrangement, disclosed in Tokukai 2005-70196, in which the photoreceptor is provided with the protective layer and (ii) the arrangement, disclosed in Tokukai 2004-86142, in which the fluorocarbon resin layer is provided as the outermost surface layer of the photoreceptor) causes the problem that electrophotographic performance, i.e., a primary function of a photoreceptor is degraded.
Further, according to the arrangement, disclosed in Tokukaihei 5-72957, in which the fluorocarbon resin is added into the edge of the blade, it is hard to realize an accurate edge of the blade which makes contact with (to be pressed against) the photoreceptor. This causes the cleaning property to be reduced.
Meanwhile, according to the arrangement, disclosed in Tokukaihei 5-72957, in which the fluorocarbon paint is applied to the edge of the blade, an area surrounding the edge can be coated, but the edge itself cannot be coated. This causes an insufficient effect of reducing a coefficient of friction. Further, the reducing effect is not retained, because the thin coating causes exfoliating of the coating or other problem to be likely to occur.
The amount of abrasion depends on line pressure (i.e., pressure at which the blade is pressed against the photoreceptor). Therefore, the amount of abrasion can be reduced by reducing the line pressure. However, when the line pressure is reduced, the toner is likely to scrape through a space between the blade and the photoreceptor. This causes the cleaning property to be reduced. On the other hand, when the line pressure is increased giving priority to a cleaning property, a turnover phenomenon occurs (i.e., the blade is turned over), so that a cleaning property is reduced after all.
Recently, small-particle toner has been used for the purpose of obtaining a high-resolution image. Particularly, among others, small-particle toner produced, for example, by a polymerization method is spherical, and it is easy to carry out a shape control of the small-particle toner by which control the cleaning property is considered. Therefore, such toner has been widely used.
Conventionally, when a blade cleans small-particle toner, the motion of the blade sensitively follows the rotation of a photoreceptor. That is, it is preferable that the blade have a high restitution coefficient. However, it has been found that: since the blade has a high coefficient of friction with respect to the photoreceptor, the blade is caused to jump up and down. This results in that a cleaning property cannot be ensured.